Multiprotocol Label Switching (MPLS) enables efficient delivery of a wide variety of differentiated, end-to-end services. Multiprotocol Label Switching (MPLS) traffic engineering (TE) provides a mechanism for selecting efficient paths across an MPLS network based on bandwidth considerations and administrative rules. Each label switching router maintains a TE link state database with a current network topology. Once a path is computed, TE is used to maintain a forwarding state along that path.
As described in more detail in various Internet Engineering Task Force (IETF) Request for Comment (RFC), such as RFC4726 and RFC5151, an Area Border Router (ABR) is a router located between several areas in a hierarchical Open Shortest Path First (OSPF) network. ABRs maintain topology information from multiple areas. In the case of Resource Reservation Protocol (RSVP) Inter-Domain TE-LSPs of type Contiguous LSP each Area Border Router (ABR) triggers a path computation (also referred to as an ERO expansion), before forwarding the RSVP Path message downstream. Thus, each ABR is responsible for calculating TE constrained path for its successive TE-Domain(s) or Area(s). Every such ABR that triggers path a computation for its TE-Domain can have multiple equal-cost paths and has to choose one of them.
In the case where equal cost multiple paths (ECMP) exist for a constrained MPLS TE-LSP which uses RSVP as a signaling protocol, a tie-breaking process to select a particular path is typically used. There are various well known and understood techniques used for tie-breaking of multiple equal-cost paths. The tie-breaking process is executed at the Head-End node where MPLS TE-LSP is configured and Constrained Shortest Path First (CSPF) computation is exercised.
Unfortunately, at present there is no way to cause all the ABRs to select a common type of tie-breaking procedure for ECMP paths such that redundant MPLS TE LSPs would have similar end-to-end paths such that TE constraints are balanced.